Stick or insect?
Northern Walkingsticks sometimes cause serious defoliation of hardwood trees.
No, this Bug of the Week is not about Lesley Hornby, the skinny English super-model. Twiggy refers to a remarkable group of insects that bring a whole new meaning to the phrase “masters of disguise.” A few weeks ago, while taking a hike on beautiful Sugar Loaf Mountain near Comus, Maryland I was amazed to see maples, hickories, and oaks stripped of foliage by some unseen horde of late season defoliators. Close inspection revealed packs of cleverly disguised Northern Walkingsticks hiding in plain sight on the branches of trees. Walkingsticks are also known as stick insects or leaf insects in various parts of the world. They are the longest extant insects on the planet with some Asian species reaching about two feet in length. Our local walkingsticks don’t quite measure up to those Asian giants but at almost four inches, these rascals are among the longest insects found in Maryland. They make their living eating foliage of trees and shrubs. In some years they are quite abundant and actually defoliate patches of trees, especially along rocky ridgetops.
Although lacking the tough armor of beetles and evasive flight of butterflies, they have perfected the art of crypsis, that is, they have an uncanny resemblance to features of their environment. This ruse of looking like branches of the trees on which they feed helps them avoid detection by hungry predators. In addition to having greatly elongated body regions and appendages matching the colors and textures of twigs, walkingsticks move and pose in ways designed to fool sharp-eyed predators. As walkingsticks search for leaves, they sway slowly back and forth mimicking the movement of a branch in the breeze. When not feeding or actively moving about, they assume a branch-like position with the front pair of legs extended directly forward. Their ability to hold an unflinching pose for hours is the envy of every mime.
When threatened by bug geeks or predators, walkingsticks may sway back and forth like branches in a breeze.
Unlike many adult insects, the Northern Walkingstick never develops wings and the nymphs and adults are quite similar in appearance. Some species of stick insects lay eggs on plants while others simply deposit them on the ground. For the Northern Walkingstick, winter is spent in the egg stage. A southern cousin of Northern Walkingstick is the longest insect in the United States and measures about half a foot. When camouflage fails to fool a hungry predator, walkingsticks may have another trick up their twig. Several species, including the Twostriped Walkingstick we met in a previous episode, have evolved glands on their thorax that emit foul smelling and irritating chemicals to foil attacks by their enemies.
Attack by the giant fingernail turns this walkingstick into a running stick.
With autumn in full force and leaves mostly fallen, spotting walking sticks in Maryland may have to wait until next year. But on your late summer hikes keep an eye open for these skinny masters of disguise.
References
Bug of the Week thanks eagle-eyed Dr. Shrewsbury for spotting and photographing walkingsticks in this episode. To learn more about these fascinating creatures, please visit the following web site:
http://www.na.fs.fed.us/spfo/pubs/fidls/walkingstick/walkingstick.htm